<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			/* var num;
			console.log(num);// undefined
			console.log(typeof(num));// undefined
			num = null; 
			console.log(num);// null
			console.log(typeof(num));// object
			
			num = 3.14;
			console.log(num);// 3.14
			console.log(typeof(num));// number
			
			num = "Hello JS";
			console.log(num); // Hello JS
			console.log(typeof(num));// string 
			*/
		   
		   /* 
		   全等：===
		   不全等：!== */
		   var m = "3";// string
		   var n = 3;// number
		   if(m == n) {// == 只是比较值是不是相等
			   console.log("m==n");
		   }
		   
		   if(m === n) {// === 值一样，类型也要一样
			   console.log("m===n");
		   }
		</script>
	</body>
</html>
